The work described in this thesis features the study of planetary materials, including nakhlite martian meteorites, comet 81P/Wild2 grains, and asteroid Itokawa 25143 particles, using various electron microscopy techniques and X-ray spectroscopy. Transmission electron microscopy (TEM), Fe-K X-ray absorption spectroscopy (XAS) and in-situ Transmission X-ray Diffraction (XRD) have been used to determine the structure, ferric content and stoichiometry in the secondary phase mineral assemblages of the nakhlites. By measuring the energy position of the Fe-K XANES 1s→3d pre-edge transition centroid, the Fe3+-rich nature of these minerals has been shown. Analyses of the crystalline phyllosilicates in Lafayette found trioctahedral ferric saponite with a 2:1 T-O-T lattice structure and d001-spacings of 0.96 nm, as well as Fe-serpentine with a 1:1 T-O structure and d001-spacings of 0.7 nm. A ferric poorly crystalline or amorphous gel of similar composition to the phyllosilicates was found as fracture fills throughout the other nakhlites. XRD and Fe-K XAS also allow the mineralogical identification of comet Wild2 terminal grains. The terminal grains of Tracks #170 and #176 are Fe-metal, with hematite subgrain material in #170. The terminal grain of #170 also includes Cr-bearing silicate, similar to the Cr-bearing terminal grain of Track #177. Olivine was found amongst the terminal grains of Track #178 alongside magnetites. The presence of magnetite is consistent with low temperature water-rock interaction similar to a carbonaceous chondrite matrix. XAS has also been used to study Itokawa particles, finding ferrous olivines and pyroxenes, as well as studying other metals and Ni-bearing phases. Comparisons with the Tuxtuac meteorite showed the similarity of Itokawa particles to that of LL5 and LL6 chondrite materials. Measuring Fe-K XAS and XRD has proved to be an effective and non-destructive method for mineralogical characterisation of planetary samples, and determining the oxidation state of Fe-silicates, especially on a micron scale. These will be essential techniques for future sample return missions and meteorite finds.

Spinal networks, once considered an inflexible ensemble of excitatory and inhibitory components organised into fixed circuits, are in fact modulated by a range of neuromodulators which impart levels of flexibility that permit adaptation to changing environments. In this thesis the roles of two known neuromodulators, nitric oxide (NO) and dopamine (DA), have been examined within the developing zebrafish nervous system. In the first results chapter, the anatomical and functional effects of perturbing NO signalling during neuromuscular junction (NMJ) development have been investigated. This revealed that prolonged exposure to NO decreased NMJ number. Additionally, miniature end plate current (mEPC) frequency was reduced, kinetics slowed, and locomotor drive affected, suggesting NO is a potent modulator of NMJ maturation and function. In the second and third chapters, the physiological maturation and functional roles of a population of DAergic neurons which project to spinal networks have been studied. To understand when and how cellular activity patterns develop, targeted in vivo electrophysiological recordings were made from dopaminergic diencephalospinal neurons (DDNs) at embryonic and larval stages, where locomotor network development and output undergo profound changes. These investigations demonstrated that DDNs functionally mature during development, engaging in low frequency tonic spiking at embryonic stages which is accompanied by high frequency bursting at larval stages. Paired recordings of DDNs with spinal neurons revealed that at free swimming (larval) stages, tonic spiking is associated with periods of locomotor inactivity, whereas bursts are associated with periods of swimming. Ablation of DDNs was sufficient to suppress locomotor output suggesting that these cells modulate spinal network excitability. In sum, these investigations provide important insights into the roles of NO and DA during locomotor network ontogeny: NO modulates NMJ maturation while DA contributes to locomotor output.

Space-borne methane observations provide increased spatial coverage and complement the precise, but sparse network of in-situ measurement sites. In this study, a method has been developed to investigate regional-scale methane budgets using space-borne methane observations, utilising the UK Met Office Numerical Atmospheric Modelling Environment (NAME). Lagrangian atmospheric dispersion models, such as NAME, allow us to investigate fluxes at a lesser computational cost and potentially, a higher spatial resolution. An inversion algorithm was created and tested on synthetic ground measurement data. The NAME based inversion algorithm was then developed to utilise column CH4 concentrations, with an intention of applying it to Greenhouse Gases Observing SATellite (GOSAT) observations. A study utilising synthetic GOSAT-like observations was carried out, as well as synthetic inversions quantifying the performance of future methane sensing space-borne missions (CarbonSat and Sentinel-5 Precursor), when used to study fluxes over the British Isles. The results were obtained for 2 months, January and July, 2011. Sentinel-5 Precursor can reduce the flux uncertainty over England by 30% over England and Wales in July, with the remaining regions (Scotland, Republic of Ireland, Northern Ireland and northern France) achieving a reduction of 8-14%. In contrast, CarbonSat error reduction values are expected to range from 3% to 18%. Finally, we used the forward model to relate bottom-up inventories to satellite observations of atmospheric XCH4 from GOSAT. For selected regions, we have inferred patterns in atmospheric XCH4 from the spatial distribution of the surface emissions, factoring in the atmospheric transport using an atmospheric dispersion model. The forward model was found to perform poorly over Western Europe (r=0.43) and North America (r=0.48). The agreement between the observations and simulations of r=0.72 were calculated over South America, r=0.60 over South East Asia and r=0.60 over Australasia.

The Infrared Atmosperhic Sounding Interferometer (IASI) provides significant impact to numerical weather prediction systems despite current assimilation schemes using less than 2% of the channels. The current system does not achieve the information content predicted by earlier theoretical studies and results presented here show that the information content could be doubled if the full spectrum were exploited. There is potential to improve the vertical resolution of the humidity analysis and the stratospheric temperature in particular. This thesis explores principal component (PC) compression and radiance reconstruction to compress the spectrum by over 90% whilst retaining almost the full information content. Theoretical calculations are shown that indicate PC scores and reconstructed radiances achieve close to the maximum information content, making them promising approaches for better exploitation of IASI. However, care must be taken because neglected error terms and matrix conditioning are problematic due to the way the information in the compressed observations is coupled in the vertical. New methods for choosing reconstructed radiance channels for assimilation are developed and tested, generating channel selections suitable for implementation in the Met Office operational system. The final section is concerned with the interaction between the observation information and the background error covariance matrix. This matrix can only ever be estimated, which causes the analysis to be suboptimal. If the differences between true and assumed errors are large enough, the analysis may be degraded relative to the background. Guarding against exaggeration of background errors is therefore important, and for water vapour in particular, spurious vertical structures in the stratosphere must be avoided. Increasing the spectral coverage increases the information content and reduces exposure to analysis degradation. This result is encouraging because it means that there is no greater risk to the analysis if more spectral information is provided, paving the way for assimilation of reconstructed radiances.

This thesis concerns atomic data, and it’s impact upon white dwarf model atmosphere calculations, and consequentially, the measurements made using such models. The thesis begins with a brief introduction to the history and properties of white dwarfs, the theory of radiative transfer, and the uses of white dwarfs in astronomy. A detailed spectroscopic survey of WD0501+524 (G191-B2B) is presented. 976 absorption features were detected, 947 of which have been successfully identified. ∼ 60% of the identified features were found to pertain to Fe and Ni iv-vi transitions. The potential consequences of using a limited atomic data set in model atmospheres are discussed, and other possible identifications to the unknown absorption features are queried. The Kurucz (1992) (Ku92) atomic database (containing ∼ 9, 000, 000 transitions) is supplemented by photoionisation (PI) cross section data from the Opacity Project for use in stellar atmosphere calculations. The more recent Kurucz (2011) (Ku11) database (containing ∼ 160, 000, 000 transitions) is not accompanied by PI cross section data. Calculations performed to create this data are described, and their effects on model atmosphere calculations are discussed. The Lyman/Balmer line problem, a discrepancy between the measured effective temperatures (Teff) from the Lyman/Balmer line series is considered. Teff and surface gravity (log g) measurements are made of 24 DA white dwarfs using model atmosphere grids utilising two atmospheric compositions, two Stark broadening tables, and the Ku92 and Ku11 atomic data sets. It is shown that the average opacity contributed by all metal species in the atmosphere drives the discrepancy between the measured Lyman/Balmer Teff. Analysis of Extreme Ultraviolet Explorer (EUVE) data for seven metal rich white dwarf stars is presented. Four model atmosphere grids were calculated using two atmospheric compositions (Preval et al. 2013; Barstow et al. 2003) and the Ku92 and Ku11 atomic datasets. Improved fits for wavelengths shortward of 230°A are obtained for all stars except WD0501+524, where significant discrepancies remain.

The thesis concerns the assessment of the performance of the upcoming Earth Cloud Aerosols Radiation Explorer (EarthCARE) Doppler cloud profiling radar in convection. Spaceborne Doppler radar data are simulated starting from high-resolution CRM model data, through forward Monte Carlo simulation from which the voltage signals as sampled by specific radar configuration are generated. Until the launch of Earth- CARE in 2016, simulations are the only means of assessing the impact of EarthCAREs configuration on the accuracy of the Doppler products (reflectivity and mean Doppler velocity). Two of the main contributors to EC-CPR total error budget are the multiple scattering and non-uniform beam filling effect errors, which can be mitigated using methods described in the thesis. However, for Earth- CARE radar using the conventional pulse pair technique, the scientific requirement for accuracy of 1 m/s at 1 km integration of Doppler velocity cannot be met for deep convective systems, even if the correction methods are applied. The thesis then focuses on six polarization diversity radar systems, three for W-band (94 GHz) and three for Ka-band (35 GHz). After the correction methods are applied for MS and NUBF effects, the accuracy of 1 m/s for 500 m integration is possible for all W-band configurations assessed. This includes relatively small antennas of 2.5 m currently being implemented in space. Consequently, two key results for measurements in deep convection can be drawn for future radar concept design. Firstly, the large antenna will help to minimize the effects of non-uniform beam filling and multiple scattering. Secondly, the polarization diversity can solve the problem of aliasing of velocities.

We show that rotational line spectra of molecular clusters with near zero permanent dipole moments can be observed using impulsive alignment. Aligned rotational wave packets were generated by non-resonant interaction with intense femtosecond laser pump pulses and then probed using Coulomb explosion by a second, time-delayed femtosecond laser pulse. By means of a Fourier transform a rich spectrum of rotational eigenstates was derived. Guided by ab initio calculations for the smallest cluster comprising of a single acetylene molecule and a helium atom, essentially all rotational eigenstates up to the dissociation threshold could be established, providing a comprehensive picture of the rotational energy level structure. The C2H2-He complex is found to exhibit distinct features of large amplitude motion and very early onset of free internal rotor energy level structure.

Gamma-ray bursts (GRBs) are the most luminous transient events in the Universe, and as such are associated with some of the most extreme processes in nature. They come in two types: long and short, nominally separated either side of a two second divide in gamma-ray emission duration. The short class (those with durations of less than two seconds) are believed to be due to the merger of two compact objects, most likely neutron stars. Within this population, a small subsection exhibit an apparent extra high-energy emission feature, which rises to prominence several seconds after the initial emission event. These are the extended emission (EE) bursts. This thesis investigates the progenitors of the EE sample, including what drives them, and where they fit in the broader context of short GRBs. The science chapters outline a rigorous test of the magnetar model, in which the compact object merger results in a massive, rapidly-rotating neutron star with an extremely strong magnetic field. The motivation for this central engine is the late-time plateaux seen in some short and EE GRBs, which can be interpreted as energy injection from a long-lived central engine, in this case from the magnetar as it loses angular momentum along open field lines. Chapter 2 addresses the energy budget of such a system, including whether the EE component is consistent with the rotational energy reservoir of a millisecond neutron star, and the implications the model has for the physical properties of the underlying magnetar. Chapter 3 proposes a potential mechanism by which EE may arise, and how both classes may be born within the framework of a single central engine. Chapter 4 addresses the broadband signature of both short and EE GRBs, and provides some observational tests that can be used to either support or contradict the model.

In this thesis, the damage caused by space radiation on the Swift X-ray telescope CCD is investigated. The analysis reveals the presence of damaged pixels affected by charge traps that results in the degradation of the detector energy resolution. The software developed for the trap mapping analysis is presented. The implementation of the trap corrections recovers a significant fraction of the lost resolution. Data from XRT calibration radioactive sources are analysed to characterise the energy and temperature dependence of the charge losses. The trap measurements are exploited in the attempt to derive the value of the ionisation energy of silicon using a novel statistical method. The large charge losses affecting the damaged pixels are at odds with expectations from CCD irradiation by protons, that should generate single electron defects. Neutrons, instead, generated on board the XRT in the detector aluminium proton shield, may displace multiple lattice atoms, as they interact directly with the nuclei. The two scenarios were investigated exposing the same kind of CCD on board the XRT, irradiated before the Swift launch with 10 MeV protons, to a dose of 14 MeV neutrons comparable to that of the XRT during a few years in orbit, as derived from simulations developed using ESA’s space radiation modelling system. A laboratory program was undertaken at the Leicester Camera test facility to investigate the damage caused by protons and neutrons. In both cases, pixels affected by large energy losses are identified and characteristic trap energy levels are derived. In the context of satellite missions using CCDs, the observed spatial nonuniformity of the damage suggests that the classical approach of an average correction for the charge transfer inefficiency applied over the entire detector is not accurate and may produce misleading results. Optimisation of the CCD shielding design is discussed based on this investigation.

Blueshifted AGN absorption lines indicate outflowing material from the central engine. Many repeat spectral observations of AGN have observed variability in the shape and strength of these lines, however there is no scientific consensus regarding the dominant mechanism which drives this variability. The main purpose of this thesis is to investigate this mechanism in a sample of BALQSOs and a Seyfert 1 galaxy. The BALQSO sample consists of 50 quasars, in which we test the dependence of broad absorption line variability on several variables. To do this a novel technique is used (Non-negative matrix factorisation) to reconstruct the entire emission profile, allowing accurate measurement of variability even in cases of absorption line overlap with the corresponding broad emission line. No significant correlations between variability and any of the investigated properties are found. The lack of luminosity correlation suggests ionisation changes do not play a dominant role in the variability of the BALQSO population. The most variable BALQSO in the 50 quasar sample, SDSS J113831.4+351725.3, shows extraordinary BAL variability, with one C IV BAL lying outside the random walk model which accurately predicted the BAL behaviour in a large BAL study. Co-ordinated BAL changes in this object, despite being separated by thousands of km s−1, together with results of photoionisation simulations and the behaviour of the continuum, strongly suggest that the variability mechanism is ionisation fraction changes driven by variations in the input ionising continuum. The Seyfert 1 galaxy NGC 4151 is noted for its continuum variability, however its absorption line variability is less well studied. Examination of the variability of metastable helium absorption lines, which are sensitive to high column densities, suggests a crossing-clouds scenario in which changes to the line-of-sight covering fraction occur, thereby driving spectral changes. Photoionisation calculations suggest a mass outflow rate which is too small to result in galaxy feedback effects.